opencv saving image captured from webcam - c++

Question

I receive an error "SIGABRT ERROR" when the code is trying to save the image on the HD.
I'm working with a MacBook Pro Mountain Lion on last XCODE and the libraries are well reconfigured.
Someone has a solution or some ideas?
#include "cv.h"
#include "highgui.h"
#include <stdio.h>
using namespace cv;
// A Simple Camera Capture Framework
int main() {
CvCapture* capture = cvCaptureFromCAM( CV_CAP_ANY );
if ( !capture ) {
fprintf( stderr, "ERROR: capture is NULL \n" );
getchar();
return -1;
}
// Create a window in which the captured images will be presented
cvNamedWindow( "mywindow", CV_WINDOW_AUTOSIZE );
// Show the image captured from the camera in the window and repeat
while ( 1 ) {
// Get one frame
IplImage* frame = cvQueryFrame( capture );
if ( !frame ) {
fprintf( stderr, "ERROR: frame is null...\n" );
getchar();
break;
}
cvShowImage( "mywindow", frame );
// Do not release the frame!
if ( (cvWaitKey(10) & 255) == 's' ) {
CvSize size = cvGetSize(frame);
IplImage* img= cvCreateImage(size, IPL_DEPTH_16S, 1);
img = frame;
cvSaveImage("matteo.jpg",&img);
}
if ( (cvWaitKey(10) & 255) == 27 ) break;
}
// Release the capture device housekeeping
cvReleaseCapture( &capture );
cvDestroyWindow( "mywindow" );
return 0;
}

Answer 1

The problem is that you are mixing your pointer syntax. You are creating a new IplImage with IplImage* img= cvCreateImage(size, IPL_DEPTH_16S, 1); but on the following line, you lose this structure as you overwrite the pointer img with frame.
The code causing your sigabrt is where you're sending a pointer to a pointer in
cvSaveImage("matteo.jpg",&img);. You should not do &img as img already is a pointer. The following is correct:
cvSaveImage("matteo.jpg",img);
There is actually no reason for you to create a new IplImage unless you want to do some preprocessing before saving it to file.
I modified your if-clause to the following which works fine on my computer:
if ( cvWaitKey(10) < 0 ) {
cvSaveImage("matteo.jpg",frame);
}

Answer 2

I have spent several days searching the internet for the right solution with simple keyboard input. There was always some lag / delay while using cv::waitKey.
The solution I have found is with adding Sleep(5) just after capturing the frame from webcam.
The below example is a combination of different forum threads.
It works without any lag / delay. Windows OS.
Press "q" to capture and save the frame.
There is a webcam feed always present. You can change the sequence to show the captured frame / image.
PS "tipka" - means "key" on the keyboard.
Regards, Andrej
#include <opencv2/opencv.hpp>
#include <iostream>
#include <stdio.h>
#include <windows.h> // For Sleep
using namespace cv;
using namespace std;
int ct = 0;
char tipka;
char filename[100]; // For filename
int c = 1; // For filename
int main(int, char**)
{
Mat frame;
//--- INITIALIZE VIDEOCAPTURE
VideoCapture cap;
// open the default camera using default API
cap.open(0);
// OR advance usage: select any API backend
int deviceID = 0; // 0 = open default camera
int apiID = cv::CAP_ANY; // 0 = autodetect default API
// open selected camera using selected API
cap.open(deviceID + apiID);
// check if we succeeded
if (!cap.isOpened()) {
cerr << "ERROR! Unable to open camera\n";
return -1;
}
//--- GRAB AND WRITE LOOP
cout << "Start grabbing" << endl
<< "Press a to terminate" << endl;
for (;;)
{
// wait for a new frame from camera and store it into 'frame'
cap.read(frame);
if (frame.empty()) {
cerr << "ERROR! blank frame grabbed\n";
break;
}
Sleep(5); // Sleep is mandatory - for no leg!
// show live and wait for a key with timeout long enough to show images
imshow("CAMERA 1", frame); // Window name
tipka = cv::waitKey(30);
if (tipka == 'q') {
sprintf_s(filename, "C:/Images/Frame_%d.jpg", c); // select your folder - filename is "Frame_n"
cv::waitKey(10);
imshow("CAMERA 1", frame);
imwrite(filename, frame);
cout << "Frame_" << c << endl;
c++;
}
if (tipka == 'a') {
cout << "Terminating..." << endl;
Sleep(2000);
break;
}
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}